An Institute of Electrical and Electronics Engineers (IEEE) 802.16 working group has conducted a research on a high speed wireless Internet service in a broadband wireless access communication system. The broadband wireless access communication system is distinguished into an Orthogonal Frequency Division Multiplexing (OFDM) scheme and an Orthogonal Frequency Division Multiple Access (OFDMA) scheme.
A procedure of network entry of an MS in a general broadband wireless communication system is described. As being powered on, the MS receives a preamble of a DownLink (DL) frame broadcasted in a Base Station (BS) and acquires a system synchronization with the BS. Then, the MS analyzes a DL Channel Descriptor (DCD) message, an UpLink (UL) Channel Descriptor (UCD) message, a DL_MAP message, and a UL_MAP message, and acquires a DL and UL Media Access Control (MAC) synchronization with the BS.
After that, the MS transmits an initial ranging Code Division Multiple Access (CDMA) code acquired through the UCD message to the BS, receives a ranging-response (RNG-RSP) message from the BS to adjust timing and power, and acquires a ranging synchronization with the BS. Next, the MS transmits a ranging-request (RNG-REQ) message to the BS and receives an RNG-RSP message from the BS in response to the RNG-REQ message to set a basic management connection and primary management connection with the BS. Here, the BS can perform an admission control as to whether to permit or reject an MS's network entry. That is, because the RNG-REQ message includes a MAC address of an MS, the BS can store a list of MAC addresses of MSs whose entries are permitted by the BS or store a list of MAC addresses of MSs whose entries are rejected by the BS. In this case, the BS can perform the admission control using the list of MAC addresses.
Then, the MS performs an authentication operation with the BS and acquires an encryption key (i.e., a Traffic Encryption Key (TEK)) allocated to the MS. At this time, the BS can perform an admission control over the MS. That is, the MS communicates with an authentication server through contents within an authentication message. The BS can receive a notification of its result from the authentication server and perform the admission control on the MS.
After that, the MS sends a registration request to the BS and, upon registration completion, performs basic traffic connection (i.e., default transport connection) setup for transmitting/receiving a control message of an upper layer and performs Internet Protocol (IP) connection setup, thereby completing a network entry procedure.
Alternatively, the MS performs handover whenever there is a change of a cell area in the broadband wireless access communication system. A handover procedure is described. The MS receives information on neighboring BSs from a serving BS that provides a service. On the basis of this information, the MS measures a broadcast signal delivered from the serving BS and broadcast signals delivered from the neighboring BSs, and sends a handover request to the serving BS. At this time, when the MS sends the handover request, the serving BS inquires of the neighboring BSs if a handover of the MS is acceptable to the neighboring BSs.
The neighboring BSs determine if the handover of the MS is acceptable to the neighboring BSs, and report its results to the serving BS. The serving BS gathers information on neighboring BSs enabling handover from the neighboring BSs, and delivers the gathered information to the MS through a handover response message. Here, the neighboring BS can perform an admission control on the MS. In this case, the neighboring BS identifies a service level of the MS intending for handover, and performs an admission control on the basis of the existence or absence of resources utilizable in a corresponding cell. Alternately, on the basis of a MAC address of the MS, the neighboring BS can perform the same admission control as an admission control in an MS's initial entry procedure.
After that, the MS selects a target BS among neighboring BSs enabling handover, performs synchronization with the target BS, and performs a ranging procedure. Here, like the network entry procedure, at the time of performing the ranging procedure, the BS can identify the MAC address of the MS, and perform the admission control on the MS.
As described above, a BS can perform an admission control on an MS in a network entry procedure or handover procedure.
However, in the conventional ranging procedure, a ranging codes group used between an MS and a BS is fixed and thus, the BS suffers a serious hindrance from a jamming signal by a malicious MS. That is, if the malicious MS seamlessly transmits a meaningless ranging code to attack a BS, the BS cannot make preparations for this attack and in addition, is difficult to provide a smooth service to a non-malicious MS. Also, in a conventional admission control way, the BS cannot perform admission control determination until being at least allocated resources necessary for a ranging procedure from an MS.